Macroscopic fiber comprising single-wall carbon nanotubes and acrylonitrile-based polymer 
and process for making the same

ABSTRACT

The present invention relates to a high modulus macroscopic fiber comprising single-wall carbon nanotubes (SWNT) and an acrylonitrile-containing polymer. In one embodiment, the macroscopic fiber is a drawn fiber having a cross-sectional dimension of at least 1 micron. In another embodiment, the acrylonitrile polymer-SWNT composite fiber is made by dispersing SWNT in a solvent, such as dimethyl formamide or dimethyl acetamide, admixing an acrylonitrile-based polymer to form a generally optically homogeneous polyacrylonitrile polymer-SWNT dope, spinning the dope into a fiber, drawing and drying the fiber. Polyacrylonitrile/SWNT composite macroscopic fibers have substantially higher modulus and reduced shrinkage versus a polymer fiber without SWNT. A polyacrylonitrile/SWNT fiber containing 10 wt % SWNT showed over 100% increase in tensile modulus and significantly reduced thermal shrinkage compared to a control fiber without SWNT. With 10 wt % SWNT, the glass transition temperature of the polymer increased by more than 40° C.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. provisional application, Ser.No. 60/392,955, filed Jul. 1, 2002, which application is incorporatedherein by reference.

This invention was made with. United States Government support underGrant No. N00014-01-1-0657 awarded by the Office of Naval Research andpartial support from Grant No. F49620-00-1-0147 awarded by the Air ForceOffice of Scientific Research. Government may have certain rights in theinvention.

FIELD OF THE INVENTION

This invention relates generally to single-wall carbon nanotubes, moreparticularly to macroscopic fibers comprising single-wall carbonnanotubes and acrylonitrile-containing polymers.

BACKGROUND OF THE INVENTION

Polymers containing acrylonitrile are important commercial polymers foruse in fibers for such applications as fabrics, carpets and carbonfibers. High performance acrylic fibers produced from polyacrylonitrilecopolymers are used as precursors for carbon fibers. The tensile modulusof the final carbon fiber has a linear relationship with the modulus ofthe polyacrylonitrile precursor fiber.

Single-wall carbon nanotubes (SWNT), commonly known as “buckytubes,”have exceptional and unique properties, including high tensile strength,high modulus, stiffness, thermal and electrical conductivity. SWNT arefullerenes consisting essentially of sp²-hybridized carbon atomstypically arranged in hexagons and pentagons. Multi-wall carbonnanotubes are nested single-wall carbon cylinders and possess someproperties similar to single-wall carbon nanotubes. However, sincesingle-wall carbon nanotubes have fewer defects than multi-wall carbonnanotubes, the single-wall carbon nanotubes are generally stronger andmore conductive.

However, the full potential of the properties of single-wall carbonnanotubes have not been fully realized when incorporated in othermaterials due to the difficulty of dispersing the nanotubes. Theproblems associated with dispersing single-wall carbon nanotubes are duelargely to their insolubility in most common solvents and theirpropensity to rope together in SWNT bundles and be held tightly togetherby van der Waals forces. The lack of significant enhancement inmechanical properties in nanotube-polymer composites has been attributedto the weak interface between the nanotubes and the composite matrix.Therefore, methodology is needed to produce nanotube-polymer composites,and, in particular, fibers which capture the exceptional mechanicalproperties of single-wall carbon nanotubes. Fabrication of high modulusfibers containing single-wall nanotubes remains a major challenge.

SUMMARY OF THE INVENTION

In one embodiment, the present invention relates to a macroscopic fibercomprising single-wall carbon nanotubes and polymer, wherein the polymeris an acrylonitrile-containing polymer, and the fiber has across-sectional dimension of at least about 1 micron. In anotherembodiment, an acrylonitrile-containing polymer/SWNT macroscopiccomposite fiber is made by suspending SWNT in a solvent to form aSWNT-solvent suspension, admixing an acrylonitrile-containing polymerwith the SWNT-solvent suspension to form a polymer-SWNT dope, spinningthe polymer-SWNT dope to form a polymer-SWNT fiber, and drawing thepolymer-SWNT fiber to form a macroscopic drawn polymer-SWNT fiber.

In another embodiment, a macroscopic fiber comprising SWNT and anacrylonitrile-containing polymer is prepared by mixing SWNT and anacrylonitrile-containing polymer in a solvent to form a polymer-SWNTdope, spinning the polymer-SWNT dope to form a polymer-SWNT fiber, anddrawing the polymer-SWNT fiber to form a macroscopic drawn polymer-SWNTfiber.

In one embodiment of the invention, an acrylonitrile-containing polymercomposite fiber containing about 10 wt % SWNT exhibited a 100% increasein tensile modulus and a significantly reduced thermal shrinkage ascompared to a control fiber without SWNT. With 10 wt % SWNTincorporation in an acrylonitrile-containing polymer/SWNT composite, theglass transition temperature is shifted higher by about 40° C. relativeto the unfilled polymer. In drawn fibers, SWNT provides a means forincreasing the orientation and modulus of an acrylonitrile-containingpolymer fiber.

High strength and high modulus fibers comprising single-wall carbonnanotubes are useful in a variety of applications, including, but notlimited to carbon fiber production, fabrics for body armor, such asbullet-proof vests, and fibers for material reinforcement, such as intire cord and in cement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an optical micrograph of 150 mg SWNT dispersed in 100 gdimethyl acetamide (DMAc).

FIG. 1B shows an optical micrograph of 150 mg SWNT and 5 gpoly(acrylonitrile-co-methyl acrylate) (P(AN/MA) copolymer) dispersed in100 g DMAc.

FIG. 1C shows an optical micrograph of 150 mg SWNT and 15 g P(AN/MA)copolymer dispersed in 100 g DMAc.

FIG. 2 shows typical tensile curves for P(AN/MA) and P(AN/MA)/SWNTfibers.

FIG. 3 shows plots of loss factor (tan δ) as a function of temperaturefor P(AN/MA) and P(AN/MA)/SWNT composite fibers.

FIG. 4 shows plots of storage modulus (E′) of P(AN/MA) and P(AN/MA)/SWNTcomposite fibers as a function of temperature.

FIG. 5 shows thermal shrinkage (measured at 0.38 MPa stress) in P(AN/MA)and P(AN/MA)/SWNT composite fibers as a function of temperature.

FIG. 6A shows the cross-section of a P(AN/MA) copolymer fiber.

FIG. 6B shows the cross-section of a 95/5 P(AN/MA)/SWNT composite fiber.

FIGS. 7A, 7B, and 7C show SEM micrographs showing fracture behavior ofP(AN/MA) and P(AN/MA)/SWNT composite fibers.

FIG. 8A shows a SEM micrograph of the inner structure of a P(AN/MA)fiber. Arrow indicates fiber axis direction.

FIG. 8B shows a SEM micrograph of the inner structure of a 95/5P(AN/MA)/SWNT composite fiber. Arrow indicates fiber axis direction.

FIG. 8C shows a SEM micrograph of the inner structure of a 90/10P(AN/MA)/SWNT composite fiber. Arrow indicates fiber axis direction.

FIG. 9 shows tangential mode Raman spectra of a 90/10 P(AN/MA)/SWNTcomposite fiber at 0-, 45- and 90-degree angles between the fiber axisand polarization direction. The VV-0 (0-degree) orientation correspondsto a fiber axis parallel to the plane of infrared polarizationdirection. The VV-90 (90-degree) orientation corresponds to the fiberaxis perpendicular to the plane of polarization direction.

FIG. 10 shows polarized IR spectra of a P(AN/MA) fiber with thedirection of polarization at 0-degrees (parallel) to the fiber axis and90-degrees (perpendicular) to the fiber axis.

FIG. 11 shows polarized IR spectra of a 99/1 P(AN/MA)/SWNT compositefiber with the direction of polarization at 0-degrees (parallel) to thefiber axis and 90-degrees (perpendicular) to the fiber axis.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The macroscopic fibers of this invention generally encompass drawnfibers having cross-sectional dimensions in the range of about 1 micronand about 100 microns, more typically in the range of about 1 micron andabout 50 microns, and more typically in the range of about 10 micronsand about 20 microns.

Single-wall carbon nanotubes can be made from any known means, such asby gas-phase synthesis from high temperature, high pressure carbonmonoxide, catalytic vapor deposition using carbon-containing feedstocksand metal catalyst particles, laser ablation, arc method, or any othermethod for synthesizing single-wall carbon nanotubes. The single-wallcarbon nanotubes obtained from synthesis are generally in the form ofsingle-wall carbon nanotube powder.

In one embodiment, single-wall carbon nanotube powder is purified toremove non-nanotube carbon, such as amorphous carbon and metalliccatalyst residues. Metals, such as Group VIB and/or VIIIB, are possiblecatalysts for the synthesis of single-wall carbon nanotubes. Aftercatalysis, the metallic residues may be encapsulated in non-nanotubecarbon, such as graphitic shells of carbon. The metallic impurities mayalso be oxidized through contact with air or by oxidation of thenon-nanotube carbon during purification.

Purification can be done by any known means. Procedures for purificationof single-wall carbon nanotubes are related in International PatentPublications “Process for Purifying Single-Wall Carbon Nanotubes andCompositions Thereof,” WO 02/064,869, published Aug. 22, 2002, and “GasPhase Process for Purifying Single-Wall Carbon Nanotubes andCompositions Thereof,” WO 02/064,868 published, Aug. 22, 2002, andincorporated herein in their entirety by reference. In one embodiment,the nanotubes are purified by heating at 250° C. in air saturated withwater vapor. The heating is done for a length of time so as to oxidizeat least some of the non-nanotube carbon, and, may, to some extent,oxidize the metal impurities. The oxidation temperature can be in therange of 200° C. and about 400° C., preferably about 200° C. to about300° C. The oxidation can be conducted in any gaseous oxidativeenvironment, which can comprise oxidative gases, such as oxygen, air,carbon dioxide, and combinations thereof. The concentration of theoxidative gases can be adjusted and controlled by blending withnitrogen, an inert gas, such as argon, or combinations thereof. Theduration of the oxidation process can range from a few minutes to days,depending on the oxidant, its concentration, and the oxidationtemperature. After oxidatively heating the nanotubes, the nanotubes aretreated with acid to remove metallic impurities. In one embodiment, thenanotubes are slurried in the acid, which can be a mineral acid, anorganic acid, or combinations thereof. Examples of acids that could beused to treat and slurry the nanotubes include, but are not limited to,hydrochloric acid, hydrofluoric acid, hydrobromic acid, hydroiodic acid,sulfuric acid, oleum, nitric acid, citric acid, oxalic acid,chlorosulfonic acid, phosphoric acid, trifluoromethane sulfonic acid,glacial acetic acid, monobasic organic acids, dibasic organic acids, andcombinations thereof. The acid used can be a pure acid or diluted with aliquid medium, such as an aqueous and/or organic solvent. Generally, anaqueous solvent is preferred. Concentrated aqueous hydrochloric acid ispreferred for removing metallic impurities. After acid treating, theacid and impurities are removed from the nanotubes by rinsing. Thenanotubes can be rinsed with water, an organic solvent or a combinationthereof.

The single-wall carbon nanotubes can be optionally derivatized with oneor more functional groups. The carbon nanotubes can be derivatized ontheir ends or sides with functional groups, such as alkyl, acyl, aryl,aralkyl, halogen; substituted or unsubstituted thiol; unsubstituted orsubstituted amino; hydroxy, and OR′ wherein R′ is selected from thegroup consisting of alkyl, acyl, aryl aralkyl, unsubstituted orsubstituted amino; substituted or unsubstituted thiol, and halogen; anda linear or cyclic carbon chain optionally interrupted with one or moreheteroatom, and optionally substituted with one or more ═O, or ═S,hydroxy, an aminoalkyl group, an amino acid, or a peptide. Typically,the number of carbon atoms in the alkyl, acyl, aryl, aralkyl groups isin the range of 1 to about 30, and in some embodiments in the range of 1to about 10.

The following definitions are used herein.

The term “alkyl” as employed herein includes both straight and branchedchain radicals; for example methyl, ethyl, propyl, isopropyl, butyl,t-butyl, isobutyl, pentyl, hexyl, isohexyl, heptyl, 4,4-dimethylpentyl,octyl, 2,2,4-trimethylpentyl, nonyl, decyl, undecyl, dodecyl, thevarious branched chain isomers thereof The chain may be linear orcyclic, saturated or unsaturated, containing, for example, double andtriple bonds. The alkyl chain may be interrupted or substituted with,for example, one or more halogen, oxygen, hydroxy, silyl, amino, orother acceptable substituents.

The term “acyl” as used herein refers to carbonyl groups of the formula—COR wherein R may be any suitable substituent such as, for example,alkyl, aryl, aralkyl, halogen; substituted or unsubstituted thiol;unsubstituted or substituted amino, unsubstituted or substituted oxygen,hydroxy, or hydrogen.

The term “aryl” as employed herein refers to monocyclic, bicyclic ortricyclic aromatic groups containing from 6 to 14 carbons in the ringportion, such as phenyl, naphthyl substituted phenyl, or substitutednaphthyl, wherein the substituent on either the phenyl or naphthyl maybe for example C₁₋₄ alkyl, halogen, C₁₋₄ alkoxy, hydroxy or nitro.

The term “aralkyl” as used herein refers to alkyl groups as discussedabove having an aryl substituent, such as benzyl, p-nitrobenzyl,phenylethyl, diphenylmethyl and triphenylmethyl.

The term “aromatic or non-aromatic ring” as used herein are preferably5-8 membered aromatic and non-aromatic rings uninterrupted orinterrupted with one or more heteroatom, for example O, S, SO, SO₂, andN, or the ring may be unsubstituted or substituted with, for example,halogen, alkyl, acyl, hydroxy, aryl, and amino. Said heteroatom andsubstituent may also be substituted with, for example, alkyl, acyl,aryl, or aralkyl.

The term “linear or cyclic” when used herein includes, for example, alinear chain which may optionally be interrupted by an aromatic ornon-aromatic ring. Cyclic chain includes, for example, an aromatic ornon-aromatic ring which may be connected to, for example, a carbon chainwhich either precedes or follows the ring.

The term “substituted amino” as used herein refers to an amino which maybe substituted with one or more substituents, for example, alkyl, acyl,aryl, aralkyl, hydroxy, and hydrogen.

The term “substituted thiol” as used herein refers to a thiol which maybe substituted with one or more substituents, for example, alkyl, acyl,aryl, aralkyl, hydroxy, and hydrogen.

In one embodiment, the SWNT are optionally purified. The optionallypurified SWNT are dried. Drying can be done in a vacuum or in a drygaseous environment, such as air, carbon dioxide, nitrogen, inert gas,or combinations thereof. Preferably, the drying is done in a vacuum or adry gas environment without the presence of water vapor.

Suitable drying temperatures are chosen to remove adsorbed moisture. Ina vacuum environment, drying temperatures of at least 100° C. aresuitable. Preferably, the drying temperature is about 110° C.

Drying time is dependent on the drying temperature and dryingenvironment. The preferred drying time is chosen to remove adsorbedmoisture from the nanotubes.

After drying, the nanotubes are kept free from moisture, such ascontained in ambient air, and in one embodiment, dispersed in a solvent.Preferably, the solvent used is also a solvent that can be used tosolubilize acrylonitile polymers and copolymers. Dimethyl formamide(DMF) and dimethyl acetamide (DMAc) are examples of solvents that can beused to suspend or solubilize polyacrylonitrile polymers and copolymers.Other examples of organic compounds solvents that can be used to suspendpolyacrylonitrile polymers and copolymers include such solvents asdimethylsulfoxide (DMSO), ethylene carbonate, dioxanone,chloroacetonitrile, dimethyl sulfone, propylene carbonate,malononitrile, succinonitrile, adiponitrile, γ-butyrolactone, aceticanhydride, ε-caprolactam, bis(2-cyanoethyl)ether,bis(4-cyanobutyl)sulfone, chloroacetonitrile/water, chloroacetonitrile,cyanoacetic acid, dimethyl phosphate, tetramethylene sulfoxide,glutaronitrile, succinonitrile, N-formylhexamethyleneimine,2-hydroxyethyl methyl sulfone, N-methyl-β-cyanoethylformamide, methylenedithiocyanate, N-methyl-α,α,α,-trifluoroacetamide, 1-methyl-2-pyridone,3,4-nitrophenol, nitromethane/water (94:6), N-nitrosopiperidine,2-oxazolidone, 1,3,3,5-tetracyanopentane,1,1,1-trichloro-3-nitro-2-propane, and p-phenol-sulfonic acid. Otherexamples of solvents include, but are not limited to, inorganicsolvents, such as aqueous concentrated acids, e.g. concentrated nitricacid (approximately 69.5 wt % HNO₃) and concentrated sulfuric acid(approximately 96 wt % H₂SO₄), and concentrated salt solutions, e.g.zinc chloride, lithium bromide and sodium thiocyanate.

Mixing means to disperse the nanotubes in the solvent include, but arenot limited to, sonication, such as with a bath sonicator, homogenation,such as with a bio-homogenizer, mechanical stirring, such as with amagnetic stirring bar, and combinations thereof. Other mixing means caninclude high shear mixing techniques.

In one embodiment, heat can be applied to facilitate dispersing thenanotubes. At atmospheric pressure, heat can be applied up to theboiling point of the solvent.

The time of mixing is dependent on various parameters, including, butnot limited to, the solvent, temperature of the mixture, concentrationof the nanotubes and mixing means. The mixing time is the time needed toprepare a generally homogeneous nanotube-solvent suspension ordispersion.

After dispersing the SWNT in the selected solvent to form ananotube-solvent suspension, some of the solvent can optionally beremoved. Solvent removal can be achieved by any known means, such aswith the application of heat, application of a vacuum, ambient solventevaporation, or combinations thereof. The time and temperature needed toadjust the concentration of the nanotube-solvent suspension aredependent on various parameters, including, but not limited to, theparticular solvent used, the amount of solvent to be removed, and thenature of the solvent.

In one embodiment, an acrylonitrile-containing polymer is added to thenanotube-solvent suspension. Acrylonitrile-containing polymers includecopolymers containing acrylonitrile monomer and at least one othermonomer. The term “copolymer” also includes terpolymers and otherpolymers having more than two different monomers. Examples ofacrylonitrile-containing polymers include, but are not limited to,polyacrylonitrile, poly(acrylonitrile-methyl acrylate),poly(acrylonitrile-methacrylic acid), poly(acrylonitrile-acrylic acid),poly(acrylonitrile-itaconic acid), poly(acrylonitrile-methylmethacrylate), poly(acrylonitrile-itaconic acid-methyl acrylate),poly(acrylonitrile-methacrylic acid-methyl acrylate),poly(acrylonitrile-vinyl pyridine), poly(acrylonitrile-vinyl chloride),poly(acrylonitrile-vinyl acetate), and combinations thereof. A preferredacrylonitrile-containing polymer is poly(acrylonitrile-co-methylacrylate), designated as P(AN/MA) herein. For carbon fiber applications,acrylonitrile copolymers containing an acid monomer (e.g. acrylic acid,methacrylic acid, itaconic acid) are preferred.

The relative amounts of comonomer components in an acrylonitrilecopolymer, as well as the molecular weight of theacrylonitrile-containing polymer, are dependent on the end-useapplication. For applications involving carbon fiber precursors, theacrylonitrile monomer incorporation is generally greater than about 85wt %. For many fiber applications, the acrylonitrile monomerincorporation can be in the range of about 35 wt % and about 85 wt %.The molecular weight of acrylonitrile-containing polymer is highlydependent on the desired processing conditions and end-use application.Typically, the molecular weight range of an acrylonitrile-containingpolymer is in the range of about 30,000 g/mole and about 200,000 g/mole.For carbon fiber applications, the molecular weight of the acrylonitrilepolymer is generally in the range of about 70,000 g/mole and about200,000 g/mole. However, there are other applications, in which themolecular weight of the acrylonitrile-containing polymer could rangebelow 30,000 g/mole and above 200,000 g/mole and into the millions, forexample, ultra-high molecular weight acrylonitrile-containing polymers.

In one embodiment, an acrylonitrile-methyl acrylate copolymer with a90:10 AN:MA comonomer ratio and a M_(n) molecular weight of about100,000 g/mole is an example of a polymer suitable for preparing themacroscopic fiber of present invention.

The polymer concentration in the particular solvent is dependent onvarious factors, one of which is the molecular weight of theacrylonitrile-containing polymer. The concentration of the polymersolution is selected to provide a viscosity conducive to the selectedfiber spinning technique. Generally, with respect to the preparation ofa polymer solution, the polymer molecular weight and polymerconcentration are inversely related. In other words, the higher themolecular weight of the polymer, the lower the concentration of polymerneeded to obtain the desired viscosity. For example, solutions up toabout 25 wt % could be made with an acrylonitrile polymer having amolecular weight on the order of about 50,000 g/mole. Likewise,solutions up to about 15 wt % polymer could be made with anacrylonitrile-containing polymer having a molecular weight of about100,000 g/mole. Likewise, solutions up to about 5 wt % polymer could bemade with acrylonitrile-containing polymer having a molecular weight ofabout 1,000,000 g/mole. The solution concentrations would also dependon, among other variables, the particular polymer composition, theparticular solvent, and solution temperature.

In one embodiment, the acrylonitrile-containing polymer is added to aSWNT-solvent suspension and homogenized to form an optically homogeneouspolymer-SWNT solution or suspension, also called “dope”. Preferably, thepolymer is in a form, such as a powder or small granules, to facilitatesolubilization of the polymer. The polymer can be added all at one time,gradually in a continuous fashion or stepwise to make a generallyhomogeneous solution. Mixing of the polymer to make anoptically-homogeneous solution can be done by any known means, such asmechanical stirring, such as with a magnetic stirrer, sonication,homogenization, high shear mixing, single- or multiple-screw extrusion,or combinations thereof.

In another embodiment of the present invention, the single-wall carbonnanotubes and the polymer can be mixed with the solvent simultaneouslyrather than stepwise. In such case, the acrylonitrile-containingpolymer, SWNT and solvent are mixed to form an optically homogenouspolymer-SWNT dope. Mixing of the nanotubes and polymer to make anoptically-homogeneous solution can be done by any known means, such asmechanical stirring, such as with a magnetic stirrer, sonication,homogenization, high shear mixing, single- or multiple-screw extrusion,or combinations thereof.

After preparation of the generally homogeneous polymer-SWNT dope, thedope can be spun into a polymer-SWNT fiber by any known means of makingdrawable, macroscopic fibers. Examples of techniques for making drawablefibers include, but are not limited to, gel spinning, wet spinning, dryspinning and dry-jet wet spinning. After the polymer is extruded throughthe spinneret, the fiber is drawn in a manner consistent with theparticular spinning technique used. For dry-jet wet spinning, the fiberis coagulated and cooled under tension in one or more liquid bathscontaining various amounts of the solvent used in the dope and anon-solvent, such as water. Generally, the initial baths will have ahigher solvent-to-non-solvent ratio than the later baths. The last bathcan contain only non-solvent. The fiber is then heated above its T_(g),e.g. to approximately the extrusion temperature, in another bath. Thetension on the heated fiber is provided by a take-up roll, the speed ofwhich is adjusted to achieve the desired draw ratio. The spinning anddrawing causes the polymer molecules and nanotubes to be substantiallyaligned. Some of the nanotubes and polymer chains are in intimatecontact and can intertwine; and as a result of this contact, anacrylonitrile-containing polymer/SWNT composite fiber is produced thateither does not fibrillate or exhibits only minimal amounts offibrillation.

In one embodiment of the invention, a polymer-SWNT fiber is prepared bydry-jet wet spinning a polymer-nanotube dope. In this embodiment, thepolymer-nanotube dope is heated for a length of time prior to spinningthrough a spinneret. The fiber passes through the spinneret and throughan air gap before entering a wet coagulation bath. In one embodiment,the fiber enters multiple coagulation baths. The coagulation bathscontain varying amounts of the same solvent used in the polymer-nanotubedope and water. In each subsequent bath, the ratio of solvent to wateris decreased such that the final bath contains only water. In each bath,tension is applied by adjusting a take-up roll speed. The temperature ofeach bath is selected to achieve the desired effect. For example, thefirst bath temperature is selected to coagulate and rapidly cool thefiber, and, as such, is set at a temperature lower than the extrusiontemperature. In order to draw the fiber, the temperature of the fiber iselevated to a temperature above the polymer's glass transitiontemperature (e.g. above about 95° C. for polyacrylonitrile), which canbe done by adjusting the bath temperature. In one embodiment, the fiberis drawn in a heated bath containing a high boiling point solvent, suchas glycerol (b.p. 290° C.). At this elevated temperature, the take-uproll speed can be adjusted to elongate the fiber to achieve the desireddraw ratio of the fiber. Typical draw ratios for wet spinning, dryspinning and dry-jet wet spinning are typically in the range of 10 timesto 20 times the length of the undrawn fiber. Typical draw ratios for gelspinning are in the range of about 30 times and about 100 times thelength of the undrawn fiber. In one embodiment, the macroscopic drawnfiber has a length in the range of about 2 times and about 100 times thelength of the polymer-SWNT fiber before drawing.

After the fiber exits the final bath, it is dried under-tension.Polyacrylonitrile-containing polymers can be dried up to about 170° C.in a variety of media, such as, but not limited to, air, nitrogen, inertgases and combinations thereof. A typical drying temperature is about120° C. for a time on the order of seconds. The drying time can varydepending on a number of factors, including, but not limited to, thesize of the fiber, the number of fibers in the tow, the solvent used inthe dope of the fiber, and the drying temperature. Tow is a term thatmeans a multifilament fiber formed from the spinning of multiplefilaments simultaneously. In certain embodiments, the single-wall carbonnanotubes are present in the drawn polymer-SWNT fiber in a range ofabout 0.001 wt % and about 50 wt %, about 1 wt % and about 25 wt %, orabout 5 wt % and about 15 wt %. At least some of the single-wall carbonnanotubes are present in the macroscopic fiber as ropes of single-wallcarbon nanotubes.

Drawn acrylonitrile-containing polymer/SWNT composite macroscopic fibershave exhibited higher tensile and storage modulus, higher solventresistance, greater alignment and tensile strength than a comparablefiber without SWNT.

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples which follow representtechniques discovered by the inventors to function well in the practiceof the invention, and thus can be considered to constitute preferredmodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention.

EXAMPLE 1

This method demonstrates the preparation of a spinning dope of purepolyacrylonitrile-co-methyl acrylate (P(AN/MA) in dimethyl acetamide(DMAc) solvent. Total solids were 15 g in 100 g DMAc.

100 g DMAc was added to a 250-ml sample bottle and cooled to 0 to 5° C.using an ice jacket. About 30 mg oxalic acid, which is about 0.2% of thepolymer weight, was added as an anti-gelling agent. 15 g finely powderedP(AN/MA) polymer from Sigma Aldrich, having a 90:10 acrylonitrile:methylacrylate comonomer ratio and a M_(n) molecular weight of about 100,000g/mole, was added step-wise to the DMAc in small quantities underconstant stirring. The stirring was continued until the all of thepolymer was dissolved and the solution was clear and opticallytransparent. This solution was used to make the polyacrylonitrile(P(AN/MA) control fiber.

EXAMPLE 2

Preparation of PAN-SWNT Solutions in DMAc

This example demonstrates the preparation of spinning dopes containingpoly(acrylonitrile-co-methyl acrylate) (P(AN/MA)) and single-wall carbonnanotubes (SWNT) at different P(AN/MA):SWNT weight ratios in DMAc. Foreach P(AN/MA):SWNT ratio prepared in this example, the acrylonitrilecopolymer, obtained from Sigma Aldrich, contained a 90:10 AN:MAcomonomer ratio and a M_(n) molecular weight of about 100,000 g/mole.For each preparation in this example, single-wall carbon nanotubes (LotNo. HPR87), were obtained from Rice University, where they were made ina high temperature, high pressure, all-gas phase process through thedisproportionation of carbon monoxide (CO) to SWNT and CO₂ using iron asthe transition metal catalyst. Furthermore, for each preparation in thisexample, sonication was done with a bath sonicator (Cole-Parmer Model8891R-DTH), and homogenation was done with a bio-homogenizer (BiospecProducts Inc., Bartlesville, Okla., Model 133/1281-0). Total solids foreach polymer/SWNT combination were 15 g in 100 g DMAc.

99:1 P(AN/MA):SWNT in DMAc

0.15 g purified and dried SWNT (Lot HPR87) and 30 mg oxalic acid weremixed with 250 mls DMAc and sonicated two hours using a bath sonicator.During sonication, the mixture was stirred every half hour with abio-homogenizer for at least 2 to 3 minutes. The solution was thentransferred to a round bottom flask. The excess solvent was boiled off(at 166° C.) to give a final volume of about 107 mls, which weighednearly 100 g. The dispersion obtained did not settle for several days,however, optical microscopy studies showed some nanotube inhomogeneity,as seen in FIG. 1A. To this dispersion, 5 g P(AN/MA) copolymer was addedstepwise in small quantities and stirred well until dissolved. Thissolution, shown in FIG. 1B, had better nanotube dispersion than theSWNT-only suspension. To the resulting solution, 9.85 g more P(AN/MA)copolymer was added, stirred and dissolved to get a solution consistingof 100 g DMAc, 14.85 g P(AN/MA) and 0.15 g SWNT, shown in FIG. 1C.Compared to FIGS. 1A and 1B, the solution shown in FIG. 1C is veryhomogeneous.

95:5 P(AN/MA):SWNT in DMAc

0.75 g purified, dried SWNT and 30 mg oxalic acid was mixed with 250 mlsDMAc and sonicated for two hours using a bath sonicator. Duringsonication, the mixture was stirred every half hour with abio-homogenizer for at least 2-3 minutes. The solution was thentransferred to a round bottom flask and the excess solvent was boiledoff (at 166° C.) to a give a final volume of about 107 mls,. whichweighed nearly 100 g. The dispersion did not settle for several days,however, optical microscopic studies show the solution was nothomogenous. To this dispersion 5 g P(AN/MA) copolymer was added stepwisein small quantities and stirred well to dissolve. This solution showed abetter dispersion of nanotubes. To the resulting solution 9.25 g moreP(AN/MA) copolymer was added and stirred and dissolved to get a solutionconsisting of 100 g DMAc, 14.25 g P(AN/MA) and 0.75 g nanotubes. Theresulting solution was very homogeneous.

90:10 P(AN/MA):SWNT in DMAc

1.5 g purified, dried SWNT and 27 mg oxalic acid were mixed with 250 mlsDMAc and sonicated for two hours using a bath sonicator. Duringsonication, the mixture was stirred every half hour with abio-homogenizer for at least 2-3 minutes. The solution was thentransferred to a round bottom flask and the excess solvent boiled off(at 166° C.) to give a final volume of about 107 mls, which weighednearly 10 g. To this dispersion, 5 g P(AN/MA) copolymer was addedstepwise in small quantities and stirred well until complete dissolved.To the resulting solution, 8.5 g more copolymer was added, stirred anddissolved to get a solution consisting of 100 g DMAc, 13.5 g P(AN/MA)and 1.5 g nanotubes.

85:15 P(AN/MA):SWNT in DMAc

2.25 g purified and dried SWNT and 25 mg oxalic acid were mixed with 250mls DMAc and sonicated for two hours using a bath sonicator. Duringsonication, the mixture was stirred every half hour with abio-homogenizer for at least 2-3 minutes. The solution was thentransferred to a round bottom flask and the excess solvent boiled off(at 166° C.) to give a final volume of about 107 mls, which weighednearly 100 g. To this dispersion, 5 g P(AN/MA) copolymer was addedstepwise in small quantities and stirred well to dissolve. This solutionshowed a better nanotube dispersion than the dispersion withoutP(AN/MA). To the resulting solution, 7.75 g more copolymer was added,stirred and dissolved to get a solution consisting of 100 g DMAc, 12.75g P(AN/MA) and 2.25 g nanotubes.

EXAMPLE 3

This example demonstrates the preparation of polyacrylonitrile-co-methylacrylate, P(AN/MA), in dimethyl formamide (DMF) without nanotubes. Thetotal solids are 15 g in 100 g DMF.

100 g DMF was added to a 250-ml bottle and cooled to 0 to 5° C. using anice jacket. About 30 mg oxalic acid, about 0.2% of the polymer weight,was added as an anti-gelling agent. 15 g finely powdered P(AN/MA)copolymer (90:10 AN:MA comonomer ratio and M_(n)˜100,000 g/mole obtainedfrom Sigma Aldrich) was added stepwise in small quantities underconstant stirring. The stirring was continued until the entire polymerwas dissolved and formed a clear, transparent solution. This solutionwas used make a control polyacrylonitrile (PAN) fiber.

EXAMPLE 4

Preparation of PAN-SWNT Solution in DMF

This example demonstrates the preparation of spinning dopes containingpoly(acrylonitrile-co-methyl acrylate) (P(AN/MA)) and single-wall carbonnanotubes (SWNT) at different P(AN/MA):SWNT weight ratios in DMF. Ineach case in this example, the acrylonitrile copolymer, obtained fromSigma Aldrich, had a 90:10 AN:MA comonomer ratio and a M_(n) molecularweight of about 100,000 g/mole. In this example, the single-wall carbonnanotubes were prepared by different processes. In each preparation inthis example, sonication was done with a bath sonicator (Cole-ParmerModel 8891R-DTH), and homogenation was done with a bio-homogenizer(Biospec Products Inc., Bartlesville, Okla., Model 133/1281-0). Totalsolids for each polymer/SWNT combination were 15 g in 10 g DMF.

95:5 P(AN/MA):HIPCO® SWNT in DMF

HIPCO® single-wall carbon nanotubes (SWNT Lot HPR 87) were obtained fromRice University where they were made in a high temperature, highpressure, all-gas phase process through the disproportionation of carbonmonoxide (CO) to SWNT and CO₂ using iron as the transition metalcatalyst.). (HIPCO is a registered trademark of Carbon Nanotechnologies,Inc., Houston, Tex.) 0.75 g purified, dried nanotubes and 30 mg oxalicacid, which is about 0.2 wt % of the polymer, were mixed with 250 mlsDMF and sonicated for two hours using a bath sonicator. Duringsonication, the mixture was stirred every half hour with abio-homogenizer for at least 2 to 3 minutes. The solution was thentransferred to a round bottom flask and the excess solvent was boiledoff to a final volume of about 107 ml, which weighed nearly 100 g. Thedispersion obtained did not settle for several days, however, opticalmicroscopy studies showed nanotube inhomogeneity. To this dispersion 5 gP(AN/MA) copolymer was added stepwise in small quantities and stirredwell to dissolve. This solution showed better nanotube dispersion thanwithout added polymer. To the resulting solution, 9.25 g more copolymerwas added, stirred and dissolved to get a solution consisting of 100 gDMF, 14.25 g P(AN/MA) and 0.75 g nanotubes.

95:5 P(AN/MA):Laser Oven SWNT in DMF

Single-wall carbon nanotubes (SWNT Lot CNI PO 42600s) were obtained fromCarbon Nanotechnologies, Inc., Houston, Tex., where they were preparedby a laser oven method using a graphite target and a nickel-cobaltcatalyst. 0.75 g purified, dried nanotubes and 30 mg oxalic acid, whichwas about 0.2 wt % of the polymer, were mixed with 250 mls DMF andsonicated for two hours using a bath sonicator. During sonication, themixture was stirred every half hour with a bio-homogenizer for at least2-3 minutes. The solution was then transferred to a round bottom flaskand the excess solvent boiled off to get a final volume of about 107 ml,which weighed nearly 100 g. The dispersion obtained did not settle forseveral days, however, optical microscopy studies showed that thesolution was not homogenous. To this dispersion, 5 g P(AN/MA) copolymerwas added stepwise in small quantities and stirred well untildissolution. This solution showed a better dispersion of nanotubes. Tothe resulting solution, 9.25 g more copolymer was added, stirred anddissolved to get a solution consisting of 100 g DMF, 14.25 g P(AN/MA)and 0.75 g nanotubes.

93:7 P(AN/MA):Unpurified HIPCO® SWNT in DMF

Single-wall carbon nanotubes (SWNT Lot HPR 87) were obtained from RiceUniversity where they were made in a high temperature, high pressure,all-gas phase is process through the disproportionation of carbonmonoxide (CO) to SWNT and CO₂ using iron as the transition metalcatalyst. 1.05 g dried, unpurified nanotubes and 30 mg oxalic acid weremixed with 250 mls DMF and sonicated for two hours using a bathsonicator. During sonication, the mixture was stirred every half hourwith a bio-homogenizer for at least 2-3 minutes. The solution was thentransferred to a round bottom flask and the excess solvent boiled off toproduce a final volume of about 107 mls, which weighed nearly 100 g. Thedispersion did not settle for several days, however, optical microscopystudies showed that the solution was not homogenous. To the dispersion,5 g P(AN/MA) copolymer was added stepwise in small quantities andstirred well until dissolved. The nanotubes of the resulting mixturewere better dispersed than the nanotube dispersion without polymer. Tothe resulting mixture, 8.95 g more copolymer was added, stirred anddissolved to get a solution, or dope, consisting of 100 g DMF, 13.95 gP(AN/MA) and 1.05 g nanotubes. The final dispersion obtained was veryhomogeneous and free from any solid chunks.

EXAMPLE 5

This example demonstrates the preparation of fiber from the P(AN/MA) andP(AN/MA)/SWNT dopes made in Examples 1, 2, 3, and 4. All fibers wereprepared by dry-jet wet spinning using a spinning machine manufacturedby Bradford University Research Ltd. having a single hole spinneret of500-μm diameter. Each dope was maintained at 80° C. and filtered througha 635-mesh (20-μm) stainless steel filter pack (from TWP Inc.) prior tospinning. The air gap (distance between the spinneret orifice and theliquid surface in the first coagulation bath) was about 5 cm. Thevolumetric throughput rate (Q) was 0.27 ml/min/hole to obtain a linearjet velocity <V> of 1.38 m/min. The first take-up roll speed, V, wasmaintained at 1.4 m/min to give a jet stretch, <V>/V, of nearly equalto 1. The ram speed was maintained at 0.5 mm/min. Standard spinningconditions are given in Table 1. (Draw ratio is indicated by the symbolλ. The solvent in the baths were DMAc for the DMAc-based dopes ofExamples 1 and 2 and DMF for the DMF-based dopes of Examples 3 and 4.)TABLE 1 I Bath (Coagulation bath) Composition - 60/40; Solvent/H₂OTemperature - 30° C. Take-up roll speed - 1.4 m/min. II BathComposition - 10/90; Solvent/H₂O Temperature - 30° C. Take-up rollspeed - 1.4 m/min. λ₁ = 1.0 III Bath Composition - 0/100; Solvent/H₂OTemperature - 90 ± 2° C. Take-up roll speed - 6.4 m/min. λ₂ = 4.6 DryingHeater plate temperature - 120° C. Winding speed - 6 m/min. λ₃ = 0.94Total draw ratio (TDR) = 1.0 × 4.6 × 0.94 = 4.3

The total draw ratio (λ₁×λ₂×λ₃) for the fibers made from P(AN/MA) andP(AN/MA)/SWNT dopes containing DMAc in this example was 4.3. Generally,higher draw ratios are typically used with dry-jet wet spinning.Typically, draw ratios of 10 to 20 times the undrawn fiber are used withthis spinning method. In case of P(AN/MA)/SWNT composite fibers, higherdraw ratios could be achieved with dopes containing 1 and 5 wt % SWNTversus those containing higher concentrations of SWNT.

EXAMPLE 6

Tensile and dynamic mechanical properties of fibers formed from theP(AN/MA) dope made by the procedures of Example 1 and P(AN/MA)/SWNT inDMAc dopes made by the procedures in Example 2 were measured using aRheometrics RSA III solids analyzer. The gauge length was 25 mm and thecrosshead speed was 10 mm/min.

Typical tensile curves for the fibers of P(AN/MA) and P(AN/MA)/SWNTcomposites are given in FIG. 2; and measured tensile properties arelisted in Table 2. TABLE 2 Mechanical Properties of P(AN/MA) andP(AN/MA)/SWNT composite fibers Initial Tensile Elongation TensileStrength at break Modulus Fiber Draw Ratio (GPa) (%) (GPa) P(AN/MA) 4.30.23 11.6 7.5 P(AN/MA)/SWNT 4.3 0.25 14.3 8.0 (1 wt % SWNT; HPR 87)P(AN/MA)/SWNT 4.3 0.352 11.3 13.4 (5 wt % SWNT; HPR 87) P(AN/MA)/SWNT4.3 0.33 9.9 16.3 (10 wt % SWNT; HPR 87)

The table shows that the tensile strength and modulus are improved bythe incorporation of SWNT. Compared to the P(AN/MA) control fiber, theP(AN/MA) fibers containing 5 wt % SWNT showed enhanced mechanicalproperties, tensile strength and initial modulus. P(AN/MA) fiberscontaining 10% SWNT showed an increase in modulus of over 100% and anincrease in tensile strength of over 40% versus the P(AN/MA) controlfiber.

Dynamic mechanical tests were done with a Rheometrics Scientific'ssolids analyzer (RSA III) at a frequency of 10 Hz at a heating rate of5° C./min. (Fiber shrinkage was determined using TA Instrumentsthermomechanical analyzer (TMA 2940) at 0.38 MPa pretension. Fibercross-sectional areas were determined by weighing known lengths of eachfiber. The average densities of the composite fibers were calculatedfrom the component densities and weight fractions. The densities usedfor the components were 1.18 g/cm³ for P(AN/MA) and 1.3 g/cm³ for thesingle-wall carbon nanotubes. Other properties determined for theP(AN/MA) and P(AN/MA)/SWNT composites are given in Table 3. TABLE 3Properties of P(AN/MA) and P(AN/MA)/SWNT composites Fiber cross-sectional area T_(g) Fiber (cm²) (° C.) P(AN/MA) 4.4 × 10⁻⁵ 100P(AN/MA)/SWNT 3.9 × 10⁻⁵ 114 (5 wt % SWNT; HPR 87) P(AN/MA)/SWNT 4.9 ×10⁻⁵ 141 (10 wt % SWNT; HPR 87)

FIG. 3 shows the loss factor, tan δ, as a function of temperature forthe control P(AN/MA) and 95/5 and 90/10 P(AN/MA)/SWNT composite drawnfibers. The temperature at the maximum tan δ is indicative of the glasstransition temperature T_(g). The 95/5 and 90/10 P(AN/MA)/SWNT compositedrawn fibers had T_(g)s that were 114° C. and 141° C., i.e., about 14°C. and more than 40° C. higher, respectively, than the P(AN/MA) controlfiber. The tan δ peaks for the P(AN/MA)/SWNT composites, besides beingshifted to higher temperature, were also significantly lower inamplitude and broader than the P(AN/MA) control. Although not meant tobe held by theory, the broadening of the tan δ peak and shift to highertemperature may be attributed a more constrained motion of the polymermolecules in contact or near SWNT in the polymer-SWNT composites. Thehigher glass transition temperatures in the composites are consistentwith the composites higher modulus retention at elevated temperatureswith respect to the P(AN/MA) control.

Higher modulus retention is important in many applications. For example,fiber having a high modulus above 120° C. could be useful in suchapplications as tire reinforcement. FIG. 4 shows plots of storagemodulus for the 90/10 P(AN/MA)/SWNT composite and the P(AN/MA) controlas a function of temperature. At room temperature, the storage modulusof the 90/10 P(AN/MA)/SWNT composite gave a storage modulus that wastwice that of the P(AN/MA) control. This doubling of modulus isconsistent with the higher tensile modulus measured at constant strainand given in Table 2. At the higher temperatures of 120° C. and 150° C.,the storage modulus of the 90/10 P(AN/MA)/SWNT composite was 13 timesand 12 times that of the P(AN/MA) control, respectively. The increase instorage modulus is indicative of the reinforcing effect of SWNT inP(AN/MA)/SWNT composites.

Thermal shrinkage in air was measured for P(AN/MA)/SWNT) composites andP(AN/MA) control as a function of temperature and the curves are shownin FIG. 5. At 200° C., the shrinkage in the P(AN/MA)/SWNT compositefibers was nearly half of that of the P(AN/MA) control fiber. Incontrast to the P(AN/MA) control fiber, the polymer molecules in theP(AN/MA)/SWNT composite fibers have SWNT in close contact and/orentangled with them, and, as such, are not as free to shrink as they arewithout nanotube incorporation.

The reduced shrinkage in P(AN/MA)/SWNT fibers may be useful for carbonfiber processing, in which stabilization of the polyacrylonitrileprecursor fiber is typically done between 200° C. and 300° C. in anoxidative environment. To obtain high modulus carbon fibers,stabilization is done under tension to minimize shrinkage duringstabilization. Because of their reduced shrinkage, fibers comprisingacrylonitrile-containing polymers and SWNT could reduce the tensionrequirement in the stabilization process for making carbon fibers frompolyacrylonitrile polymers, produce carbon fibers with higherorientation and modulus, or a combination thereof.

Scanning electron microscope photographs of the fiber cross-sections ofP(AN/MA) control and P(AN/MA)/SWNT composite are shown in FIGS. 6A and6B. Although both fibers were spun through the same round-holespinneret, the P(AN/MA)/SWNT composite fiber was more distorted fromround, i.e. more rectangular or oval, than the P(AN/MA) control fiberwithout SWNT. Both fibers show significant transverse cracks resultingfrom the counter diffusion of solvent and the non-solvent. Thecross-sectional morphology of the spun fibers depends on the fibercoagulation rate, and the coagulation rate depends on the temperatureand composition of the coagulation baths as well as that of the polymersolution.

Scanning electron micrographs of fiber tensile fracture surfaces showsignificant fibrillation in the control P(AN/MA) fiber as shown in FIG.7A, while the 95/5 and 90/10 P(AN/MA)/SWNT composite fibers shown inFIGS. 7B and 7C, respectively, exhibited longitudinal splitting andalmost no fibrillation. SWNT incorporation appeared to significantlyreduce or prevent fibrillation in the composite fibers. Images of thefiber fractured surfaces at higher magnification are given in FIG. 8Afor the P(AN/MA) fiber, and FIGS. 8B and 8C for the 95/5 and 90/10P(AN/MA)/SWNT composite fibers, respectively.

Whereas drawn P(AN/MA) fiber readily dissolves in solvents, such as DMFand DMAc, the P(AN/MA)/SWNT composite fibers did not completely dissolveeven after several days at room temperature, rather disintegratedmillimeter (mm) and sub-mm-size particles were observed. Solventfiltered (through a Fisherbrand P5 filter paper) was colorless,indicating that the nanotubes did not dissolve, but FTIR analysisconfirmed the presence of P(AN/MA) in the solvent. Based on residualweight analysis, about 50% of the P(AN/MA) in the 95/5 P(AN/MA)/SWNTcomposite fiber was dissolved. The rest of the polymer was presumed toremain entangled with individual SWNT or SWNT ropes and did not dissolvein DMF or DMAc.

Tangential-mode Raman spectra of the SWNT in the 90/10 P(AN/MA)/SWNTcomposite fiber were taken at 0-, 45- and 90-degree angles between thefiber axis and the polarization direction using “VV geometry”configuration. (For background information on VV geometry, see Hwang, etal., “Polarized spectroscopy of aligned single-wall carbon nanotubes,”Phys. Rev. B, 62, No. 20, Nov. 15, 2000-II, p. R13 310-313.) As shown inFIG. 9, the intensity of the peak at 1592 cm⁻¹ monotonically decreasedwith increasing angle between the fiber axis and the polarizationdirection of the polarizer, which is indicative substantial SWNTalignment in the composite fiber. Using the height of 1592 cm⁻¹ peak andbased on a Gaussian distribution, Herman's orientation factors ofP(AN/MA)/SWNT composite fibers with 1, 5, and 10 wt % SWNT at a commondraw ratio of 4.3 were calculated to be 0.90, 0.94, and 0.92,respectively, indicative of substantial nanotube alignment along thefiber axis. Herman's orientation factor (ƒ), an indicator of alignment,is given by ${f = \frac{3 < {\cos^{2}\theta} > {- 1}}{2}},$where θ is the angle between SWNT and the fiber axis. A factor of 1indicates complete alignment of the SWNT with the fiber axis.

The substantial SWNT alignment in P(AN/MA)/SWNT composite fiber was alsoconfirmed using polarized infrared (IR) spectroscopy. FIG. 10 showspolarized IR spectra in the 2000-2500 cm⁻¹ range for 4.3-draw ratioP(AN/MA) control and FIG. 11 shows polarized IR spectra in the samerange for a 99/1 P(AN/MA)/SWNT composite fiber. Both sets of spectrawere taken with the polarization directed parallel and perpendicular tothe fiber axes. Although the parallel and perpendicular polarizedspectra of P(AN/MA) control fiber are nearly identical, as shown in FIG.10, significant absorption differences were observed in the parallel andperpendicular spectra for the 99/1 P(AN/MA)/SWNT composite fiber, shownin FIG. 11. At higher nanotube loading levels, such as polymercomposites with 5 wt % nanotube incorporation, the IR absorption was sohigh that no transmitted beam was observed. Carbon nanotubes areintrinsically strong absorbers of radiation in the IR and near IRregion. As the nanotube content increases, the absorption alsoincreases, such that transmission can be completely or nearlyextinguished. At such high absorption, signals due to the polymer arenot observable. The absorption is greatest and transmission lowest whenthe nanotube axis and the polarizer are parallel to each other.

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the compositions and methods of this invention havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to thecompositions and methods and in the steps or in the sequence of steps ofthe method described herein without departing from the concept, spiritand scope of the invention. More specifically, it will be apparent thatcertain agents which are chemically related may be substituted for theagents described herein while the same or similar results would beachieved. All such similar substitutes and modifications apparent tothose skilled in the art are deemed to be within the spirit, scope andconcept of the invention as defined by the appended claims.

1. A method for making a macroscopic fiber comprising single-wall carbonnanotubes (SWNT) and an acrylonitrile-containing polymer, comprising:(a) mixing SWNT and an acrylonitrile-containing polymer in a solvent toform a polymer-SWNT dope, (b) spinning the polymer-SWNT dope to form apolymer-SWNT fiber; and (c) drawing the polymer-SWNT fiber to form adrawn polymer-SWNT macroscopic fiber.
 2. The method of claim 1 whereinthe polymer is selected from the group consisting of polyacrylonitrile,poly(acrylonitrile-methyl acrylate), poly(acrylonitrile-methacrylicacid), poly(acrylonitrile-acrylic acid), poly(acrylonitrile-itaconicacid), poly(acrylonitrile-methyl methacrylate),poly(acrylonitrile-itaconic acid-methyl acrylate),poly(acrylonitrile-methacrylic acid-methyl acrylate),poly(acrylonitrile-vinyl pyridine), poly(acrylonitrile-vinyl chloride),poly(acrylonitrile-vinyl acetate), and combinations thereof.
 3. Themethod of claim 1 wherein the polymer is selected from the groupconsisting of polyacrylonitrile, polyacrylonitrile copolymer andcombinations thereof.
 4. The method of claim 1 wherein the polymer ispoly(acrylonitrile-methyl acrylate).
 5. The method of claim 1 whereinthe polymer is poly(acrylonitrile-itaconic acid-methyl acrylate).
 6. Themethod of claim 1 wherein the polymer is poly(acrylonitrile-methylmethacrylate).
 7. The method of claim 1 wherein the single-wall carbonnanotubes are derivatized with a functional group.
 8. The method ofclaim 1 wherein the solvent is selected from the group consisting ofdimethyl formamide, dimethylsulfoxide, ethylene carbonate,dimethylacetamide, dioxanone, chloroacetonitrile, dimethyl sulfone,propylene carbonate, malononitrile, succinonitrile, adiponitrile,γ-butyrolactone, acetic anhydride, ε-caprolactam,bis(2-cyanoethyl)ether, bis(4-cyanobutyl)sulfone,chloroacetonitrile/water, chloroacetonitrile, cyanoacetic acid, dimethylphosphate, tetramethylene sulfoxide, glutaronitrile, succinonitrile,N-formylhexamethyleneimine, 2-hydroxyethyl methyl sulfone,N-methyl-β-cyanoethylformamide, methylene dithiocyanate,N-methyl-α,α,α,-trifluoroacetamide, 1-methyl-2-pyridone,3,4-nitrophenol, nitromethane/water, N-nitrosopiperidine, 2-oxazolidone,1,3,3,5-tetracyanopentane, 1,1,1-trichloro-3-nitro-2-propane,p-phenol-sulfonic acid, and combinations thereof.
 9. The method of claim1 wherein the solvent is a concentrated aqueous acid selected from thegroup consisting nitric acid and sulfuric acid.
 10. The method of claim1 wherein the solvent is a concentrated aqueous salt selected from thegroup consisting of zinc chloride, lithium bromide and sodiumthiocyanate.
 11. The method of claim 1 wherein the solvent comprisesdimethyl formamide.
 12. The method of claim 1 wherein the solventcomprises dimethyl acetamide.
 13. The method of claim 1 wherein the dopecomprises an anti-gelling agent.
 14. The method of claim 13 wherein theanti-gelling agent comprises oxalic acid.
 15. The method of claim 1wherein the spinning is done by a method selected from the groupconsisting of gel spinning, wet spinning, dry spinning, dry-jet wetspinning and combinations thereof.
 16. The method of claim 1 wherein thespinning is done by dry-jet wet spinning.
 17. The method of claim 1wherein the spinning is done by gel spinning.
 18. The method of claim 1wherein the drawn macroscopic fiber has a length in the range of about 2times and about 100 times the length of the polymer-SWNT fiber beforedrawing.
 19. The method of claim 1 wherein the single-wall carbonnanotubes are present in the drawn polymer-SWNT macroscopic fiber in arange of about 0.001 wt % and about 50 wt %.
 20. The method of claim 1wherein the single-wall carbon nanotubes are present in the drawnpolymer-SWNT macroscopic fiber in a range of about 1 wt % and about 25wt %.
 21. The method of claim 1 wherein the single-wall carbon nanotubesare present in the drawn polymer-SWNT macroscopic fiber in the range ofabout 5 wt % and about 15 wt %.
 22. The method of claim 1 wherein atleast some of the single-wall carbon nanotubes are present in themacroscopic fiber as single-wall carbon nanotube ropes.
 23. The methodof claim 1 wherein the macroscopic fiber has a cross-sectional dimensionof at least about 1 micron.
 24. The method of claim 1 wherein thepolymer-SWNT fiber has a glass transition temperature that is higherthan the glass transition temperature of the polymer.
 25. The method ofclaim 1 wherein the drawn polymer-SWNT macroscopic fiber has lessshrinkage than a drawn fiber of the polymer.
 26. The method of claim 1wherein the drawn polymer-SWNT macroscopic fiber has a greater tensilemodulus than a drawn fiber of the polymer.
 27. A method for making amacroscopic fiber comprising single-wall carbon nanotubes (SWNT) and anacrylonitrile-containing polymer, comprising: (a) suspending SWNT in asolvent to form a SWNT-solvent suspension; (b) admixing anacrylonitrile-containing polymer with the SWNT-solvent suspension toform a polymer-SWNT dope, (c) spinning the polymer-SWNT dope to form apolymer-SWNT fiber; and (d) drawing the polymer-SWNT fiber to form adrawn polymer-SWNT macroscopic fiber.
 28. The method of claim 27 whereinthe polymer is selected from the group consisting of polyacrylonitrile,poly(acrylonitrile-methyl acrylate), poly(acrylonitrile-methacrylicacid), poly(acrylonitrile-acrylic acid), poly(acrylonitrile-itaconicacid), poly(acrylonitrile-methyl methacrylate),poly(acrylonitrile-itaconic acid-methyl acrylate),poly(acrylonitrile-methacrylic acid-methyl acrylate),poly(acrylonitrile-vinyl pyridine), poly(acrylonitrile-vinyl chloride),poly(acrylonitrile-vinyl acetate), and combinations thereof.
 29. Themethod of claim 27 wherein the polymer is selected from the groupconsisting of polyacrylonitrile, polyacrylonitrile copolymer andcombinations thereof.
 30. The method of claim 27 wherein the polymer ispoly(acrylonitrile-methyl acrylate).
 31. The method of claim 27 whereinthe polymer is poly(acrylonitrile-itaconic acid-methyl acrylate). 32.The method of claim 27 wherein the polymer is poly(acrylonitrile-methylmethacrylate).
 33. The method of claim 27 wherein the single-wall carbonnanotubes are derivatized with a functional group.
 34. The method ofclaim 27 wherein the solvent is selected from the group consisting ofdimethyl formamide, dimethylsulfoxide, ethylene carbonate,dimethylacetamide, dioxanone, chloroacetonitrile, dimethyl sulfone,propylene carbonate, malononitrile, succinonitrile, adiponitrile,γ-butyrolactone, acetic anhydride, ε-caprolactam,bis(2-cyanoethyl)ether, bis(4-cyanobutyl)sulfone,chloroacetonitrile/water, chloroacetonitrile, cyanoacetic acid, dimethylphosphate, tetramethylene sulfoxide, glutaronitrile, succinonitrile,N-formylhexamethyleneimine, 2-hydroxyethyl methyl sulfone,N-methyl-β-cyanoethylformamide, methylene dithiocyanate,N-methyl-α,α,α,-trifluoroacetamide, 1-methyl-2-pyridone,3,4-nitrophenol, nitromethane/water, N-nitrosopiperidine, 2-oxazolidone,1,3,3,5-tetracyanopentane, 1,1,1 -trichloro-3-nitro-2-propane,p-phenol-sulfonic acid, and combinations thereof.
 35. The method ofclaim 27 wherein the solvent is a concentrated aqueous acid selectedfrom the group consisting nitric acid and sulfuric acid.
 36. The methodof claim 27 wherein the solvent is a concentrated aqueous salt selectedfrom the group consisting of zinc chloride, lithium bromide and sodiumthiocyanate.
 37. The method of claim 27 wherein the solvent comprisesdimethyl formamide.
 38. The method of claim 27 wherein the solventcomprises dimethyl acetamide.
 39. The method of claim 27 wherein thedope comprises an anti-gelling agent.
 40. The method of claim 39 whereinthe anti-gelling agent comprises oxalic acid.
 41. The method of claim 27wherein the spinning is done by a method selected from the groupconsisting of gel spinning, wet spinning, dry spinning, dry-jet wetspinning and combinations thereof.
 42. The method of claim 27 whereinthe spinning is done by dry-jet wet spinning.
 43. The method of claim 27wherein the spinning is done by gel spinning.
 44. The method of claim 27wherein the drawn macroscopic fiber has a length in the range of about 2times and about 100 times the length of the polymer-SWNT fiber beforedrawing.
 45. The method of claim 27 wherein the single-wall carbonnanotubes are present in the drawn polymer-SWNT macroscopic fiber in arange of about 0.001 wt % and about 50wt %.
 46. The method of claim 27wherein the single-wall carbon nanotubes are present in the drawnpolymer-SWNT macroscopic fiber in a range of about 1 wt % and about 25wt %.
 47. The method of claim 27 wherein the single-wall carbonnanotubes are present in the drawn polymer-SWNT macroscopic fiber in therange of about 5 wt % and about 15 wt %.
 48. The method of claim 27wherein at least some of the single-wall carbon nanotubes are present inthe fiber as single-wall carbon nanotube ropes.
 49. The method of claim27 wherein the macroscopic fiber has a cross-sectional dimension of atleast about 1 micron.
 50. The method of claim 27 wherein thepolymer-SWNT fiber has a glass transition temperature that is higherthan the glass transition temperature of the polymer.
 51. The method ofclaim 27 wherein the drawn polymer-SWNT macroscopic fiber has lessshrinkage than a drawn fiber of the polymer.
 52. The method of claim 27wherein the drawn polymer-SWNT macroscopic fiber has a greater tensilemodulus than a drawn fiber of the polymer. 53-66. (canceled)